Study Of Fault Characteristic Of UHV Transmission System And Improvement Of Failure Protection Of Breaker

The first AC testing demonstration project of Ultra High Voltage (UHV) in China - the 1000kV UHV transmission line project of Jindongnan,Nanyang and Jingmen has started on August 2006. The project begins from 1000kV Jingxinan Transformer Substation to Jingmen Transformer Substation via Nanyang Switch Substation. The line is about 645km, passing through Shanxi, Henan and Hubei Province. With the construction, the Ultra High Voltage attracts the notice of the whole electric power industry. The fault characteristic of line will become a hot subject of UHV system. The performance requirements of transmit electricity line and breaker will become more strict.The thesis constitutes failure simulation models of UHV transmission line on the basis of model studying of transmission line. Using Matlab to simulate and compute, the author does research on the failure states of UHV transmission line, and the results are analyzed. After comparing analyzing the breaking current under the normal and non-normal operation conditions of breaker, the usable characteristic of breaker failure protection are worked out. The way to improve the reliability and rapidity of breaker failure protection is researched, too. The works are as follows:①Constituting model of single-phase distribution transmission line from different points, based on the equations solution of long transmission line. After comparing the equivalent chain model, Bergeron model and dynamic phasor model, the author choose the equivalent chain model.②Modeling the long Ultra High Voltage (UHV) transmission lines in the environment of Matlab /Simulink, and simulating single phase short circuit, two phase short circuit, two phase short circuit to the earth and three phase short circuit at the head, middle and end of the transmission line. Simulation results are analyzed. The results show that, due to the characters of high voltage level, huge transmission capacity and long transmission line, there exists big decaying dc component which decay very slow in the short circuit current at the moment of short circuit. At the end of long transmission line, the fault current exists relatively high frequency contents.③Studying the theory of arc and using arc models in Matlab. After comparing the simulation results, the author chooses the Schwarz arc model. During the arc transient process, the high frequency content makes the line voltage distortion, which influences the precision of voltage obtaining and correct operation.④Introducing principle and operation of breaker failure protection. The scheme of breaker failure protect of UHV is proposed. The improved protection method could clear fault quicker adaptively under the condition of fault operation of circuit breaker.⑤Rebuilding the simulation model according to the improvement method and doing simulations under different fault conditions. Validity of the proposed method are improved by the simulation results.